The 570 DI and 596c HD DI use the same transducer.
The max DI depth specification for the 570 DI has not been changed yet but will be the same as the 596c HD DI unit (and all the other DI units once they get changed). Through on-water testing it was confirmed that the DI sonar in these units will perform to 350 feet deep. Not sure where this testing was done so your results may vary. So the differences in the displays these units use is the only difference.
The 596c HD DI can be made portable as well by buying the PTC-U or PTC-U NB portable kits or by making your own.
No, the Si units cannot scan the Si sonar to that water depth (so the Di sonar will not work that deep either).